Shkadov thruster

A hypothetical device built by a Type II Kardashev
civilization to control a star's motion. It consists of a mirror of
rim angle psi placed at some distance r from a star S (see
figure). The mirror causes an asymmetry of stellar radiation in the star–mirror
system and, consequently, gives rise to a net thrust on the star. For a
certain mirror of superficial mass density, a balance exists between the
gravitational force and the force due to star radiation pressure and the
mirror-star distance remains constant. It can be shown that, for a well-designed
system, the thrust could produce a significant deviation of the Solar System's
normal trajectory in the Galaxy.1